Recently, with environmental concerns on the background, hybrid vehicles and electric vehicles have attracting attention. These vehicles mount an electric motor as a driving power source, and a secondary battery, for example, is used as an electric power source. Some of these vehicles include a boosting converter provided between the secondary battery and an inverter driving the electric motor. When electric power is supplied from the secondary battery to the electric motor, the boosting converter boosts the voltage and, therefore, the electric motor can operate even if rated voltage of secondary battery is lower than the rated voltage of electric motor.
By way of example, Japanese Patent Laying-Open No. 2006-50863 discloses an example of a vehicle having a boosting converter. In the vehicle, the boosting converter boosts voltage of a DC power source and supplies the voltage to an inverter driving an electric motor. The vehicle includes a controller that calculates a voltage command value based on the speed of rotation of the electric motor and an input voltage to the inverter, and controls an output voltage of the boosting converter based on the voltage command value.
Generally, in high-voltage equipment, possibility of discharge increases as atmospheric pressure decreases. In a vehicle provided with an electric motor, it is possible that inter-phase dielectric resistance of the electric motor decreases when the vehicle runs at high altitude. A possible method of protecting the electric motor when atmospheric pressure lowers is to mount an atmospheric pressure sensor on the vehicle and to adjust the input voltage of the inverter (that is, an output voltage of boosting converter), based on the output from the atmospheric pressure sensor.
Use of such a method is on the premise that the atmospheric pressure sensor has high reliability. Japanese Patent Laying-Open No. 2006-50863 does not specifically describe a method of controlling the boosting converter in consideration of atmospheric pressure variation.